Process for making stainless clad pierced tubes



1- P. A. E. ARMSTRONG ETAL 2,258,563

. PROCESS FOR MAKING STAINLESS GLAD PIERCED TUBES I Fil ed March 11, 1940 MET/7L j lNVENTORS fizzy 17. I. firms/mil Tecumseh Jfiennaq lid;

,%ATTORNEY Patented Oct. 7, 1941 PROCESS FOR MAKING STAINLESS GLAD PIERCED TUBES Percy A. E. Armstrong, Westport, Conn., and

Tecumseh Sherman Fitch, Washington, Pan; said Fitch assignor to said Armstrong Application March 11,1940, Serial No. 323,258

1 4 Claims. (Cl. 29-188) This application relates to a method of producing composite steel tubes in which the lining is of a high melting point corrosion resistant metal such as nickel or a chromium alloy and the outer shell is a mild or low carbon steel. The composite tubes made in accordance with the process covered by this application are claimed in our divisional application Ser. No. 388,634, filed April 15, 1941.

The need for tubes of this kind has been recognized and heretofore attempts to make them have been undertaken in accordance with which an annular steel billet was prepared with a cylindrical core of corrosion resistant metal and this composite product was intended to be pierced on a standard Mannesmann mill. The 'difliculty with such a process is that the strain exerted in the piercing operation is suthcient to tear apart any bond that may exist between the cylindrical core and the outer annular shell.

In accordance with our invention, we start with a core of corrosion resistant metal which instead of being cylindrical is square in cross section, or has a cross section which is of an angular nature such as a hexagon or octagon. This is enclosed (either by casting or, preferably, in the manner later illustrated) in an outer shell of a steel which ordinarily will be corrodibie and relatively ductile such as a low carbon or low alloy steel, which is also preferably square or at least is formed with oppositely disposed flat sides which permit the composite body to be rolled between fiat faced rolls. This fiat rolling effects a weld between the core and the outer cover. In order to assure that such a weld will be accomplished,

the corrosion resistant metal (or even better, both the corrosion resistantmetal and the faces of the corrodibie metal that are to be welded with it) should first be electroplated with iron under conditions which will prevent the formation of a layer of intervening oxide as set forth in Armstrong Patent No. 1,997,538, dated April 9, 1935.

By hot rolling the original assembly or billet on its flat sides, an excellent bond or weld can be obtained between the core and the outer cover.

together. In other words, the rolling operations greatly. increase any natural bond between the two types of metal and this rolling is such as to create an interlock between the two. On the other hand, if one starts with a cylindrical core and once the bond is broken it cannot be re-.

' stored.

When a billet has been prepared in accordance with our invention, it can be passed through a Mannesmann mill and pierced without any difficulty and without any noticeable tendency for the core and covering material to separate.

Our invention can be readily" understood by reference to the accompanying drawing, in which Fig. 1 is a section of an assembly made up ready,

for rolling; Fig. 2 shows a-sectional view of the billet prior to piercing and Fig. 3 shows a perspective view of a section of the finished product.

In the drawing, I0 is a bar of stainless steel or other high melting point corrosion resistant metal (say for example a usual type of alloy ooncontaining .15% to 30% carbon) which is here shown as made up of two pieces which are welded together after having been shaped to receive bar Ill by machining or by the use of a dolly or by rolling. This assembly, after the usual heating, is passed through flat rolls first on one axis and then on another until all of the elements are welded into a substantially integral mass. Subsequently the resulting billet is passed through a usual series of rolls to reduce it to round form, after which it usually will be turned 0 machined to accurate circular cross section. f a section of the resulting round product is taken, it will be found that the stainless steel core ID has somewhat approached the circular form but still has projections as indicated at It where theformer corners originally appeared. These comers lock the core It to the casing II as shown in Fig. 2.

This billet is now passed through a usual type of Mannesmann mill in which it is pierced and ordinarily enlarged in diameter (though such an enlargement is not necessary as the reduced cross sectional area of metal may if desired be made up by increased length). If a section of the pierced tube thus formed is examined, it will be found that the comers ii are still present and that these have been given a substantial twist so that they spiral through the tube as indicated by the dotted lines l8 in Fig. 3. Ordinarily, the corrosion resistant metal is stiffer than the low carbon steel cover and the presence of these spirally arranged projections tends to stifien the whole tube to a greater extent than would be the case if the core were of uniform thickness. Apparently there is no appreciable tendency for the core and casing to separate.

As already stated, the core may have any desired number of sides, which means that it will have a corresponding number of projections such as those indicated at IS in the drawings, but the projections that remain will be found to be SP1", rally arranged as described. While we state that the core may have any desired number of sides, this statement must be given a reasonable interpretation. Naturally the number of sides must not be increased to the point where the projections of the core into the covering metal become insignificant, as it is of the very essence of our invention that the projections of the core that remain after the billet has been rolled to round form must be of suflicient magnitude to key togetherythe metal of the core and the covering metal and thereby prevent relative movement between them under the torsional strains that result from piercing operations such as those oi. the Mannesmann mill.

What we claim is:

1. The method of forming composite tubes which comprises preparing a bar of a high melting point corrosion resistant metal the cross section of which forms an angled figure, enclosing such bar in a covering of corrodible steel under conditions which will permit the bar and covering to weld together, hot working the bar and covering to effect such welding, rolling and shaping the resulting billet to form a billet having a circular cross section in which the angles of the corrosion resistant bar can still be detected as irregularities of suflicient magnitude to key together the metal of the core and the covering metal and thereby prevent relative movement between them under torsional strains, and thereafter converting such billet into a tube by a rolling and piercing operation.

2. A method as specified in claim 1 in which an octagonal bar of chromium alloy steel is enclosed by welding in an assembly of low carbon steel members which are hot rolled into a substantially integral mass.

3. A method of taming composite tubes which comprises preparing a bar of high melting point corrosion resistant metal the cross section of which forms an angled figure, electroplating the surface of such bar with iron under conditions adapted to prevent the formation of a layer of oxide, enclosing such bar in a covering 0! corrodible steel, hot working the bar and covering to cause the two to be welded together, rolling and shaping the resulting billet to form a billet having a circular cross section in which irregularities derived from the angles oi. the corrosion resistant bar can still be detected, as forming projections of suillcient magnitude to key together the metal of the core and the covering metal and thereby prevent relative movement between them under torsional strains, and thereafter converting such billet into a tube by a rolling and piercing operation.

4. A method as specified in claim 3, in which the faces of the corrodible steel covering which are to be welded to the corrosion resistant bar are likewise electroplated with iron.

PERCY A, E. ARMSTRONG. TECUMSEH SHERMAN FITCH. 

